Photonic integrated circuits (PICs) with optical waveguides having a semiconductor core, such as for example PICs based on Silicon-on-Isolator (SOI) technology, have several advantages over photonic circuits using all-dielectric waveguides. These advantages stem at least in part from the possibility of using well-developed semiconductor fabrication processes and technologies for electronic control of various properties of the waveguide material, including its refractive index and absorption coefficient. Furthermore, the refractive index of many conventional semiconductor materials may be considerably higher than that of typical dielectric materials conventionally used in optical waveguides, which enables fabricating high-index-contrast waveguides that allow for tighter waveguide bends, thereby making the optical circuits smaller. For example, functional micro-ring resonators with the radius as small as 2-3 microns (μm) have been fabricated using the SOI technology. Such micro-resonators may be useful for many applications, including high-speed modulation of light signals, wavelength filtering and multiplexing, and sensing. However, semiconductor materials that are typically used in optical waveguides, including silicon (Si), may have a relatively high thermo-optic coefficient, i.e. the rate of change of the refractive index with temperature, which may lead to sensitivity to environmental temperature variations or to operation-related thermal perturbations. Photonic circuits that require accurate control of the phase of the optical beam, such as those including micro-ring resonators and other optical elements relying on optical interference effects, may be particularly sensitive to temperature variation. For example, in the 1.5 μm wavelength range typical for telecom applications, the thermo-optic coefficient of silicon (Si)) is about 1.8×10−4 K−1, which is approximately an order of magnitude higher than that of the silicon dioxide (SiO2); as a result, the resonant wavelength of a silicon micro-ring can drift by 70-80 picometer (pm) per degree K temperature change in the telecom wavelength range, making such devices extremely vulnerable to thermal perturbations.
There is a need for semiconductor-based photonic integrated circuit devices that have improved stability and/or control with regard to thermal perturbations.